Conventionally well bores and apparatus associated with wellbores have been sealed with plugs and packers and the like. Plugs, for example, have three basic parts: an anchoring system, a seal element and a setting system.
The first stage in setting a conventional plug is anchoring the plug in the wellbore. Anchoring systems for conventional wellhead plugs use a set of locking dogs, which engage a recessed profile in the wellbore or tree, or use a set of slips which “bite” the casing to hold the plug in place.
The seal element is then set using a linear action setting mechanism to create a linear displacement to deform the seal element. The force required to create the seal is then locked in using a linear locking mechanism. In safety critical wellbore applications, for example sub sea trees, the seal is generally a metal-to-metal seal formed by swaging a metal ring element into the bore or onto a no-go shoulder.
To provide a seal capable of withstanding well pressures, the required setting force needs to be as high as the maximum force generated by the well pressure.
In recent years a number of high pressure, high temperature, high flow rate wells have been completed which have highlighted shortcomings in conventional designs of seal elements. For example, swaged seal elements can dislodge when exposed to the high pressure, temperature and vibration cycles of these wells, and the jarring action used to set the seal element can damage the seal element or the conduit or apparatus to be sealed.
A further disadvantage of conventional seal elements is that the expansion achievable from, for example, a metal seal element may not be sufficient to permit the apparatus incorporating the seal element to be run-into the wellbore with adequate clearance between the apparatus and the wellbore to prevent a build-up of pressure in front of the apparatus, resisting the placement of the apparatus. This can be a particular problem when a number of, for example, packers are to be located in series in a conduit, as a hydraulic lock can be formed between adjacent packers.
Furthermore, in cases where there is inadequate clearance, the metal seal element may engage the wellbore as the apparatus is run-in causing damage to the wellbore or to the seal element. If the seal element is damaged, this can result in an imperfect seal being formed by the seal element when the seal is set in its desired location.
In some instances, there is no clearance between the seal element and the conduit to be sealed and the seal element requires to be stabbed in which complicates running procedures and positional control.